The engine will not clear the firewall, at least mine didn't. I cut the firewall and made kniches so the engine would sit back. You don't have to do this. You can move your motor mount perches to the forward holes. If you want to use headers they will not clear the left perch and you will have to put in later model ones or aftermarket ones. I used aftermarket. You can see some pictures of stuff here.
http://67-72chevytrucks.com/vboard/s...d.php?t=259536 .. The thread seems to be shut down probably because of inactivity, but you can still read through it.